Grazing

This story by former Refuge Manager Christy Smith was originally published in the Summer 2008 issue of Tideline, the quarterly newsletter of the San Francisco Bay National Wildlife Refuge Complex.

Home on the (Antioch Dunes NWR) Range?

Those who toured Antioch Dunes National Wildlife Refuge in the spring are now able to add one more species to their species list. The vision of cows munching on grass may have startled some wildlife watchers who are familiar with the inland dune ecosystem known for its endemic rare plants and animals.

Once a large complex of riverine sand dunes, the site is now limited to 55 acres due to urban development and sand mining activities up to the establishment of the refuge in 1980. Most of the original habitat and sand substrate are gone and the site, rather than being reminiscent of dunes, is more comparable to a flat or a pit. Without active, moving sand dunes, invasive non-native plant species have the upper hand throughout the refuge. These invasive non-native plants out-compete two endemic endangered plants, the Contra Costa wallflower (Erysimum capitatum var. angustatum) and the Antioch Dunes evening primrose (Oenothera deltoiodes spp. Howellii). It also out-competes the naked stem buckwheat (Eriogonum nudum var.auriculatum) which is the host plant for the endangered Lange’s metalmark butterfly (Apodemia mormo langei).

Measures to eliminate the non-native plants over the past several years included hand pulling and chemical and mechanical controls. While these practices have worked, the invasion of non-natives has out-paced control efforts. A faster and more sustainable system of controlling invasive species was needed. Without aggressive management actions, the extinction of the Lange’s metalmark butterfly is imminent.

Grazing can be an effective management tool to reduce invasive plants and is well documented. In checkerspot butterfly habitats, grazing has been used to reduce competition while improving the condition of sites for native plant species.

Fueled by these positive outcomes, cows were introduced into Antioch Dunes NWR in March and are being monitored daily. When grazing was first considered, discussion ensued to determine which herbivore would best fit the need. The primary invading plant species that are doing the most harm to the habitat include grasses (rip-gut brome) and vetch. While sheep and goats may eat these species, they would also eat wallflower, primrose and naked stem buckwheat. Since the wallflower and primrose are endangered species and the Lange’s metalmark butterfly is completely dependent upon the buckwheat for its life cycle, our first concern was to do as little harm to those species.

Cattle are grazers, meaning they prefer grasses to other plant types. Cattle may be a viable and sustainable means of managing invasives by removing excessive duff and vegetative cover. In addition to removing excess cover, these large, heavy animals will disturb the soil in a controlled manner, creating ideal conditions for the endangered plants and the naked stem buckwheat to thrive. Grazing may reduce the competitive ability of invasive annuals so that the naked stem buckwheat will have a chance to grow and reproduce throughout the refuge, providing the needed habitat for the butterfly. Grazing is monitored closely to minimize negative effects on the endangered species, to determine the timing and frequency of grazing that is most effective, and to calculate the number of animals that is most beneficial.

The grazing experiment is exactly that, an experiment on only ten acres of the refuge. If successful, it will remove 30% of the non-native vegetative cover and provide an environment where buckwheat, primrose and wallflower will begin to establish naturally. Grazing is not expected to be a “cure-all” for controlling invasive plants, but rather another tool to complement other management efforts.